Improvement in screw-taps



RREYNQLDS.,

SCREW-TAP.

Patented Nov. 2.3, 1875.

f ivrrn STATES EDWIN REYNOLDS, OF PROVIDENCE, RHODE ISLAND.

IMPROVEMENT IN SCREW-TAPS.

Specification forming part of Letters Patent No. 170,398, date'dNovember 23, 1875; application tiled October to, 1875.

.To alt whom it may concern: Y

Be it known that I, EDWIN REYNOLDS, o Providence, in the county ofProvidence and State of Rhode Island, have invented certain Improvementsin Screw-Taps, and I do hereby declare that the following is a full,clear, and exact description of the same.

My invention relates to improvements in taps for cutting internalscrew-threads; and it consists in a novel construction of the cuttersvand the stock which carries them, and a novel combination andarrangement of the cutters and stock with relation to each other,whereby the cutters are made to always present a sharp cuttingedge, withany desired amount of clearance, and provision is made for sharpeningthe cutters when worn and whereby, also, the cutters are provided with aperfectly true bearing-surface and the proper positions of therespective threads are insured.

In carrying out my invention I construct the stock with longitudinalgrooves for the reception of the cutters, and a transverse groove,against the nails of which the inner ends of the cutters bear. Thelongitudinal grooves may be of dovetail or approximate form in theircross-section. The transverse groove mayY be near the shank or inner endof the stock, and is perpendicular to the axis of said stock; and thelongitudinal grooves terminate in said transverse groove, the inner sideof which forms a perfectly'true bearingsurface for the in ner ends ofthe cutters, and insures the proper positions of the respective threads.The cutters are each formed with a projecting or overhanging edge, whichmay be ground down in order to sharpen the faces of the cutters whenthey become worn.

The portion of the cutter beyond which the edge projects constituteswhat may be called the shank of the cutter. Thisiportion is narrowerthan the longitudinal groove, and the cutter is held in place in thegroove by means of a key inserted with it. The cutters are first placedin the longitudinal grooves, with the keys on that side of each cutterwhich is under the overhanging edge. They are then turned in a lathe,soA that their surfaces will f'orm arcs of circles concentric with theaxis of the stock, and the threads are cut on them, after which they areremoved and tempered,

vsharp cutting-edge and any desired amountof clearance, the amountdepending on the thickness of the key or the distance the cutter ismoved from the tirst position.

The accompanying drawing illustrates the manner of carrying out myinvention.

Figure 1 is an end view, showing the cutters and keys inserted iu thestockin the irst position. Fig. 2 is a similar view, showing the cuttersand keys in the second position. Fig. 3 is a side View ofthe stock andcutters. Fig. 4 is a transverse section, taken inthe line x a' of Fig.4.

The stock A is provided with a shank, a, of the usual or any suitableform, for insertion into a holder or carrier. In the surface of thestock a number of longitudinal grooves, B, are provided, for. thereception and retention of the cutters, which grooves are of approximatedovetail crosssectional form, or wider at the bottom than at the top.These longitudinal grooves may have a radial directionthat is to say,they may be so constructed that lines radial to the center of the topmay pass centrally through said grooves; but I prefer to construct saidgrooves so that one side, e, of each shall be radial, or nearly so, tothe center of the cutter-stock A, and the other side, f, tangential to acircle concentric to said center, in which case the general direction ofthese grooves may be said to be tangential, or laterally inclined, asmay be understood by reference to Figs. 1 and 2. The cutters are soplaced in the grooves that they have an inclination f'rom the centeroutward in a forward direction-or, in other words, they incline towardthe direction'in which the tap rotates when at work, as may be seen insaid Figs. l and 2, in which the direction of rotation is indicated byarrows. y

Near the shank or inner end of the stock is a transverse groove, C,which runs, entirely around the surface exactly perpendicular to theaXis ofthe stock. This groove is formed by first `turning itin a latheto a depth 'about equal to that indicated by the dotted line a." in Fig.4, and then cutting the metal therefrom so as form segmental spacesc",'the straightor dat bottom of each ot' which is on a line with thebottom of one ot the longitudinal grooves B. By this means the cuttersare provided with a iirm and perfectly true bearing-surface for theirinner ends, and as the rear or inner side ofthe groove U and segmentalspace cx are exactly perpendicular to the axis ofthe stock A, thepropel' positions of the threads on the cutters are insured. Theseobjects may Vbe accomplished in other Ways, as, for example, bydrilling` or boring holes at thepoints ot' junction ot' the longitudinalgrooves with the transverse grooves, or by cutting out the meta-l atsuch points to a width and depth only equal to that otl thelongitudinalgroove. But the form and manner herein described are convenient andeconomical in construction, and serve the desired purpose. If desired,the rear side of the groove, which forms the bearing-surface, may be ata right angle with the face of the cutter. The cutters `the key E, asshown in Fig. l, or the surface ofthe stock, as shown in Fig. 2,according to the side on Which the key is placed. The cutters, thusconstructed. are placed in the grooves of the stock, with the keys E onthe same side with the projecting edges d, so that said edges willoverlap the keys, as shown in Fig. l. The stock is then turned in alathe so asto impart to the face of each cutter a `curvature forming anarc of a circle drawn from the center oi' the stock, as indicated.v bythe dotted line ax in Fig. l, and the threads are cut in said faces,after which the cutters are removed from the stock and tempered, and arethenready for use. When the cutters are inserted in the stock for usethe keys E are placed on the opposite side of each shank, so as to causethe projecting edge d to overlap the surface of the stock, as shown inFig; 2.

-By this arrangement the shank is brought nearer to a radial positionwith relation tothe axis of the stock, in consequence of which thecutting-edge of the cutter is `placed beyond or outside of the originalcircle, ot which` its face formed an arc, While its rear portion isplaced inside of said circle, which circle is indicated by the dottedline ax' in Fig. 2, thus presenting a sharper cutting-edge with agreater amount of clearance than could be obtained if the cuttersremained in the lirstposition. The amount of clearance, and the anglepresented by the cutting-edge are governed by the thickness ofthe keyorthedistance which the cutter is moved from its rst position. By

constructing the cutter with the overlapping` edge d an importantadvantage is obtained in addition to that above described. When thecutting-edge becomes Worn the overhanging 'edge d is ground downso as tosharpen the cutting-edge, without interfering with themain body or shankot' the cutter.` i

This invention is equally applicable to taps `t'or cutting bothright-hand and left-hand threads by forming the overiapping edge d oneither side, according to the direction in which the tap is to rotate. v

What I claim as new, and desire to secur by Letters Patent, isv l. Acutter for screw-taps, provided with an overlapping edge, d, whereby theface of the cutter is made wider than its body or shank, and provisionis made for sharpening the cutting-edge, substantially as` hereindescribed.

2. The combination ofthe grooved cutterstock, the cutters laterallymovable in the grooves of said stock, and the reversible keys orlocking-pieces, the Whole combined and operating substantially as hereindescribed.

3. The combination, With the removable cutters, ot' the stock A,provided with longitudinal grooves B and a transverse groove, G,substantially as and for the purpose herein described. e

EDWIN REYNOLDS.

Witnesses: i

J oHN T. HENTHORN, NATHL. G. HERREsHoFF.

